DESCRIPTION: This Core serves as the point of entry for human subjects into the project. This Core is responsible for the clinical evaluations of patients with suspected HD, presymptomatic evaluations of individuals at risk for HD, and evaluation of patients with HDlike phenotypes. This Core maintains an extensive computerized database which is unique in its scope, duration, and number of subjects. This Core includes a weekly research clinic, in which new evaluations are performed, with subjects followed annually. This Core also contains the Longitudinal Core Study, in which a subset of the clinic population is examined and given a more extensive battery and a biannual MRI. This Core has also been responsible for the highly successful recruitment of subjects for clinical trials. The goals of this Core for this submission are to continue to evaluate affected, at risk, and HDlike subjects and recruit them into longitudinal followup, to continue to generate a body of longitudinal data on these subjects from the preclinical period all the way to death, to continue to provide more extensive testing on a subset of the cohort in the Longitudinal Core Study (which will also serve as the primary reservoir of subjects for therapeutic trials), and to develop new methods of assessment which are particularly sensitive to early HD and capable of distinguishing presymptomatic gene carriers from controls.